It is known from the prior art to use an epoxy glue to affix a ball lens of an optical submount. Usage of epoxy glue has several disadvantages:                The epoxy glue is aging and has a poor long term reliability.        The stability of the epoxy glue is strongly degreasing at higher temperatures.        The process of glueing a ball lens by means of epoxy glue is both time consuming and expensive as it is difficult to apply a tiny quantity of epoxy glue below the ball lens.        The position of the ball lens is defined with a greater tolerance in comparison to the tolerance which is achievable by anorganic attachment. This is because substantial quantity of epoxy glue is required for glueing the ball lens which creates a greater tolerant with respect to the exact position.        
As far as anorganic attachment is concerned it is also known from the prior art to utilizes an aluminum oxide bonding process: U.S. Pat. No. 5,178,319 shows compression bonding method for permanently bonding elements such as glass spheres and optical fibers to aluminum surfaces of substrates by applying pressure along with energy to the interface of the element and the aluminum. For example the glass sphere is bonded by pressing it against aluminum while heating the aluminum. As an alternative to heating acoustic energy can be applied to the sphere along with the pressure. Glass optical fibers can be bonded to aluminum surfaces in the same manner.
The publication “Aluminum oxide bonding—a method for joining oxide optical components to aluminum coated substrates”, Coucoulas et al., 1993 IEEE Conference proceedings, shows a similar method. This process requires that an aluminum layer is deposited in an processing step when the substrate is structured. Thus the aluminum layer is exposed to several aggressive processing steps such as exposure to acids, reflow at temperature around 300° C. etc. Such processing steps deteriorate the quality of the aluminum surface. This is a substantial problem, as the aluminum oxide bonding technique requires a contact between oxide such as silicium oxide and pure non-oxidized aluminum. As a consequence the quality of the aluminum oxide bond form the between the ball lens and the substrate is decreased because of such process steps to which the aluminum layer is subjected.
U.S. Pat. No. 5,124,281 describes a method for making a V groove such that a spherical lens can be precisely located within it. A laser is mounted on a planar surface of a mono crystalline silicon mounting member. A spherical lens is mounted in a mono crystalline silicon cover member which when adopted and registered to the mounting member aligns the spherical lens with the laser so that the output light can be projected along a precise predetermined path. The spherical lens is mounted in a V shaped groove which is made in the cover member by masking and etching. A second V shaped groove intersects the first groove and defines a V shaped edge in one site of the first groove. The spherical lens is than sited in the first V shaped groove such that it bears against two points of the V shaped edge and against one site wall of the first V shaped groove. The second lens is mounted in the cover member in the same manner as the first lens and directs laser light from a rare facet of the laser to mirror and then to a photo detector mounted in the cover member.
From U.S. Pat. No. 5,933,707 a further method for crystal substrate processing is known. An anisotropic silicon etchant is used in a processing stage to form precision machined features in the substrate. Prior to the use of the etchant a masked layer of organic dielectric is applied to the substrate. The dielectric protects surface features previously defined. By etching the I/Os in the final passivation prior to the deposition of solder the application of the organic dielectric protective layer and the aching of the V grooves the agent is prevented from accessing the opened I/O and the number and complexity of the patterning stages is thereby reduces.
From a technologic point of view it is preferable to change from glueing to an anorganic attachment but using the anorganic attachment with aluminum oxide and aluminum the results are not reliable. Checking the fixation with share tests the damaged pattern shows two characteristics:                First no bonding at all took place when the aluminum was already oxidized prior the actual bonding took place.        Second where the bonding took place the crack seems to appear within the aluminum layer. It seems that if the weak materials strength of the weak pure aluminum is one limiting factor of fixation.        